Gluconeogenesis Flashcards

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1
Q

What tissues rely on glucose solely as their main source of energy?

A
brain
nervous system
RBCs
testes
embryonic tissues
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2
Q

What is gluconeogenesis?

A

generation of glucose from non-carbohydrate substrates e.g pyruvate, lactate, glycerol and glucogenic amino acids

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3
Q

Where does gluconeogenesis normally occur?

A

the liver

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4
Q

Gluconeogenesis is not the reverse of glycolysis as glycolysis has 3 irreversible steps. What happens instead?

A

there are 4 bypass reactions A,B,C and D

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5
Q

What step of glycolysis are reactions A and B concerned with bypassing?

A

Step 10 - conversion of pyruvate or lactate to PEP

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6
Q

What happens in reaction A?

A

conversion of pyruvate or lactate to oxaloacetate

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7
Q

Lactate is covered to oxaloacetate in 2 steps. What are they?

A

lactate converted to pyruvate first by lactate dehydrogenase

pyruvate converted to oxaloacetate by pyruvate carboxlase

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8
Q

How is reaction A different if pyruvate is used as the original substrate?

A

oxaloacetate is converted to malate to leave the mitochondrion and then is reconverted to oxaloacetate once outside the mitochondrion

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9
Q

What happens in Reaction B of gluconeogenesis?

A

oxaloacetate is converted to PEP

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10
Q

What difference is there in the progression of reaction B of gluconeogenesis when pyruvate is used as a substrate rather than lactate?

A

lactate - oxaloactetate is converted to PEP INSIDE the mitochondrion
pyruvate - oxaloacetate is converted to PEP outside the mitochondrion

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11
Q

What step of glycolysis is Reaction C concerned with bypassing?

A

conversion of F-1,6BP to F-6-P

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12
Q

What enzyme catalyses Reaction C?

A

fructose 1,6-bisphosphatase

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13
Q

What reaction of glycolysis is Reaction D concerned with bypassing?

A

conversion of G-6-P to glucose

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14
Q

What enzyme catalyses Reaction D?

A

G-6-Phosphatase

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15
Q

How is free glucose formed?
Consider:
1. What is the usual end point for gluconeogenesis?
2. Where will free glucose be formed?

A

gluconeogenesis usually stops at G-6-P so that glucose can be ‘trapped’ in the cells
so free glucose formation will take place in the lumen of the ER

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16
Q

Where can fructose enter glycolysis?

A

at F-6-P

17
Q

How is fructose metabolised?

A

by the fructose-1-phosphate pathway
catalysed by 2 enzymes: fructose-1-phosphate aldolase
triose kinase
1 or 2 ATP used per fructose molecule converted

18
Q

Where can galactose enter glycolysis?

A

at G-6-P

19
Q

How is galactose initially metabolised?

A

converted to G-1-P through sugar nucleotide derivative, UDP galactose

20
Q

What happens in the pentose phosphate pathway?

A
produces NADPH
produces pentoses (5C sugars) that are precursors of ATP, RNA and DNA
21
Q

The pentose-phosphate pathway has 2 phases. What are they?

A
  • oxidative, irreversible bit that generates NADPH and converts G-6-P to a pentose phosphate
  • an non-oxidative, reversible bit that in converts G-6-P and pentose phosphate to form lots of different 3,4,5,6, and 7 carbon sugars
22
Q

What enzyme is involved in the irreversible step of P-P-P?

A

G-6-P dehydrogenase

23
Q

What is the function of NADPH?

A

to link catabolic and anabolic pathways
catabolic= pentose phosphate pathway picks up H
anabolic= fatty acid synthesis uses H

24
Q

What is the difference between NADP+ and NAD+?

A

they are both electron carriers
NAD+ is used in metabolism
NADP+ is used in anabolism

25
Q

Why does drinking reduce gluconeogenesis?

A

the metabolism of ethanol requires NAD+ to act as an electron carrier
but the liver needs NAD+ for gluconeogenesis for conversion of lactate to pyruvate

26
Q

What are the adverse effects of reduced gluconeogenesis?

A

can lead to lacticacidaemia (increase in blood lactate concentration)
hypoglycaemia (decreased blood glucose concentrations)

27
Q

What enzyme deficiency causes Black Water Fever?

A

G-6-P dehydrogenase